One of the enduring problems of controlling the movement of humans is that the world is large, and human ability to perceive the location of a human visually is limited by factors inherent in the process of visual acquisition of images. At the outset, it should be noted that control of movement can be either a captivity-promoting or freedom-promoting activity. For example, a person who has been abducted is moved inconsistent with his own control and in accordance with the wishes of his captors, who may secrete him and exercise that control for nefarious purposes. Alternatively, a person who is incarcerated may escape, and the ability of the authorities to return an escapee to custody may be thwarted by the escapee's ability to hide.
Various methods and systems for locating humans have been employed, with varying degrees of success. For centuries, humans have used specially trained dogs to track fugitives and lost persons. Search-and-rescue or search-and-recovery operations make use of aerial photography and visual search techniques to cover wide areas. Criminal investigation, interrogation, and detective work may lead to the acquisition of a human's location. Ankle bracelets may be used to sound an alarm when a confined person leaves the area in which he is confined, although they provide no locating capacity if the confined person leaves the area or removes the bracelet. Particularly in the case of transportation vehicles such as aircraft, boats, and cars, a homing beacon or transponder may be employed to assist in location. Radio or satellite communications may also provide assistance, and in the case of a person who has become lost in the outdoors, the Global Positioning System (GPS) and the wider availability of personal radio, radiotelephone, and satellite communications have contributed to a greater ability to find a person.
However, the systems in use to date all have drawbacks that limit their use in particular situations which have become unfortunately common.
As applied to escapees from prison custody, these systems fail because they can be actively thwarted by the escapee, or because they rely upon some past (but post-escape) location of the escapee to be known to another person, or because they are not cost-effectively nor compulsorily carried by the escapee. As applied to lost persons, these systems fail because of a lack of sufficient electrical power to run them, or because they have become damaged, or because they rely on the lost person to carry them and operate them effectively. As applied to an abducted person, in addition to the problems experienced by a “lost” person, these systems may be discovered actively thwarted by the abductor, or they may not work in sufficient time before the abductor carries out his nefarious purpose, or attempts to use them may cause the abductor to engage in violence to stop them.
In any of these cases, the failure to apprehend the location of the person of interest on a short timetable can have highly negative consequences. A prison escapee may commit additional crimes. A person lost in wilderness may die or be seriously harmed by exposure, starvation, or animal attack or other injury. A person who is abducted may become the victim of an even more serious personal violation, such as rape, torture, or murder. What is needed, then, is a system and method which fulfills at least three criteria necessary to promote the safe recovery of a lost person: (1) capability of identifying the person at a nontrivial distance; (2) undetectability to the naked eye, being concealable within or on the body; and (3) full independence from visible external systems, such as communications devices and power systems.
Various systems have been proposed which fulfill only one or two of these criteria. For example, the state of the art is well acquainted with radio-frequency identification devices (RFIDs), which can be made so small as to be undetectable to the naked eye and fully concealable, and which are independent of any power source. However, RFIDs have an extremely limited range—under present technology, only as much as 100 feet—that is trivial for the purpose to which the present invention is directed, although RFID technology may be useful for the present invention if the range can be extended. Conventional communications devices, such as radios and radiotelephones are capable of providing information at a distance, and can be fully independent, but are not readily concealable on or in the body.